1. Field of the Invention
The present invention relates to a humidity sensing apparatus having a structure capable of reducing the size thereof in which a humidity sensing portion is disposed in a gap between two opposite members.
2. Description of the Related Art
In a humidity sensing apparatus of the related art, a humidity sensing portion and an integrated circuit package, which is equipped with a sensing circuit and the like, are disposed in parallel on a substrate and are coated with a resin material. Since it is necessary to bring the humidity sensing portion into contact with gas to be measured, a measurement hole connected to the humidity sensing portion is formed on a surface of the humidity sensing apparatus.
In the structure of the humidity sensing apparatus of the related art in which the measurement hole connected to the humidity sensing portion is formed toward the outside, when dust or the like infiltrates into the measurement hole, it is difficult to accurately sense the humidity of gas. In addition, in the structure where the humidity sensing portion and the integrated circuit package are disposed in parallel on the substrate, the planar shape of the humidity sensing apparatus increases, and it is difficult to reduce the size thereof.
Japanese Unexamined Patent Application Publication No. 2008-70200 discloses a humidity sensing apparatus including: a substrate; and a sensor chip that forms a humidity sensor and is disposed on the substrate, in which the sensor chip is disposed to be opposite to the substrate with a gap interposed therebetween in a state where a moisture sensitive film faces the substrate. A land provided on the substrate is opposite to an electrode pad provided on the sensor chip, and the land and the electrode pad are joined to each other through a bump electrode so as to be electrically connected.
In addition, a region around the bump electrode is filled with an underfill formed of a resin material having moisture resistance, and the substrate and the sensor chip are fixed to each other through this underfill.
FIG. 9 of Japanese Unexamined Patent Application Publication No. 2008-70200 shows a structure in which a cavity portion with both sides surrounded by the underfill is formed between the substrate and the sensor chip, and a moisture sensitive film is connected to the outside through the cavity portion.
In the humidity sensing apparatus disclosed in Japanese Unexamined Patent Application Publication No. 2008-70200, in order to fix the substrate and the sensor chip opposite to each other, the underfill is filled thereinto in addition to the bump electrode. Therefore, the structure for fixing the substrate and the sensor chip and the fixing work thereof are complicated.
In addition, in the structure shown in FIG. 9 of Japanese Unexamined Patent Application Publication No. 2008-70200, gas is introduced into the moisture sensitive film through the small cavity portion with both sides surrounded by the underfill in a gap between the substrate and the sensor chip. Therefore, when the humidity is changed, a time difference is likely to be generated before the change affects the moisture sensitive film, and the humidity sensing response is decreased.